Foam filled tires are especially useful in applications involving industrial and off-the-road vehicles, where it is essential to maintain the vehicles in service, since time lost for repairs is very costly. It is known to fill tires with a curable and foamable elastomeric material, which, after heat curing, expands to a closed cell foam rubber composition that provides an operating pressure within the tire. Such foam filled tires are substantially deflation proof and almost indestructible from normal hazards, for example, bolts, nails, large holes, jagged curbs, sharp rocks, deep water, etc. Thus, foam filled tires substantially reduce the time such vehicles are down for repairs.
Examples of filled tires are shown and described in U.S. Pat. Nos. 3,022,810, 3,381,735, 3,650,865, 3,872,201, 4,060,578 and 6,623,580. U.S. Pat. No. 3,650,865 provides one example of filling a tire cavity with a curable and foamable elastomeric material to pressurize the tire. U.S. Pat. Nos. 3,650,865 and 6,623,580 describe methods of making a foam filled tire by inserting layers of a curable and foamable elastomeric material within a cured tire. The tire is then heated to cure the curable and foamable elastomeric material contained therein. The heat curing process can be performed either before, or after, the tire is mounted on a rim. Heating causes the layers of the curable and foamable elastomeric material to expand and form a closed cell foam rubber composition that provides an internal tire pressure.
Tires filled with such a curable and foamable elastomeric material have a damping similar to that of a pneumatic tire and thus, provide a pneumatic-like ride, which is especially important with unsprung off-the-road vehicles. Further, the performance of such foam filled tires is often superior to the performance of tires filled with other materials. However, when heat curing the elastomeric material in a larger off-the-road tire, substantial time is required for the inner-most portions of the elastomeric material within the tire casing to reach temperature and cure. Such a long curing time substantially increases the cost of manufacturing such tires, and thus, such tires suffer a price disadvantage in the market.
Therefore, there is a need for an improved foam filled tire structure and method of manufacture that reduces the cost of making a tire with a closed cell foam rubber composition.